Tunable reflective dual-band line-to-circular polarization convertor with opposite handedness based on graphene metasurfaces

In this letter, we propose a dual-band tunable reflective linear-to-circular (LTC) polarization converter, which is composed of a graphene sheet etched with an I-shaped carved-hollow array. In the mid-infrared region, two LTC bands with opposite handedness are simultaneously realized due to the excitation of the three graphene surface plasmon (GSP) modes. The band of line-to-right-circular-polarization (LTRCP) ranges from 9.87 to 11.03THz with ellipticity chi <-0.95, and from 9.69 to 11.36 THz with an axial ratio of less than 3 dB; the band of line-to-left-circular-polarization (LTLCP) ranges from 13.16 to 14.43THz with chi >0.95, and from 12.79 to 14.61 THz with an axial ratio of less than 3 dB. The tunable responses of the reflective polarizer with Fermi energy (E-f) and electron scattering time (tau) are discussed, and especially the perfect LTLCP can be changed to LTRCP with increasing E-f. Also, the influences of geometric parameters, incident angle, and polarization angle on the performances of the dual-band LTC are also investigated, and it is found that our polarizer converter shows angle insensitivity. All simulation results are conducted by the finite element method. Our design enriches the research of tunable LTC polarizers and has potential applications in integrated terahertz systems. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

Automated summary

This study proposes a dual-band tunable reflective linear-to-circular polarization converter, consisting of a graphene sheet etched with an I-shaped carved-hollow array, which can simultaneously achieve two bands of linear-to-right-circular-polarization and linear-to-left-circular-polarization. The tunable responses of the frequency bands can be achieved by adjusting the Fermi energy and electron scattering time.